1. Field
This following description relates to a capacitor type humidity sensor that may be aligned under a sensor capacitor. A reference capacitor provided in a humidity sensor is replaced with an MIM (metal-insulator-metal) capacitor or a PIP (polysilicon insulator polysilicon) capacitor.
2. Description of Related Art
As smart devices are commercialized, various sensors embedded to the device are suggested. For example, a humidity sensor may be embedded to recognize an ambient humidity.
Humidity sensors are divided into resistive humidity sensors and capacitive humidity sensors. A resistive humidity sensor measures humidity based on a change in resistance that is changed by humidity. Resistive humidity sensors are widely used because resistance humidity sensors tend to be price competitive in comparison to capacitive humidity sensors.
Recently, capacitive humidity sensors are manufactured on a semiconductor substrate in a one-chip form. Accordingly, it may be possible to obtain capacitive humidity sensors that are more price competitive than resistive humidity sensors. As a result, the use of capacitive humidity sensors is increasing. Further, capacitive humidity sensors may exhibit higher reliability, and may exhibit more linear sensor features and low affect due to temperature change, in comparison to resistive humidity sensors. A capacitive humidity sensor may operate as a capacitor type device having a humidity sensitive material such as polymer or ceramic absorbs moisture, which has permittivity that is changed in the presence of moisture. That is, a humidity sensitive layer for sensing humidity may be present inside the device, and the permittivity of the humidity sensitive layer may change when moisture is introduced through the humidity sensitive layer. As a result, the capacitance is changed, and the capacitance may be determined to determine a level of humidity.
There are many kinds of capacitors to measure a change of humidity. It is important to minimize a chip area as much as possible. Furthermore, manufacturing costs of a humidity sensor need to be minimized. The disclosure of U.S. Patent Application Publication No. US 2004/0182153 A1 to Hamamoto (“Hamamoto”) is incorporated herein in its entirety by reference.